Brown the sausage: Heat a large deep skillet over medium-high. Add sausage (and olive oil if needed). Cook, breaking it up, until browned and crisp at the edges, 6–8 minutes.
Spoon off excess grease, leaving about 1 tablespoon in the pan.
Sauté the aromatics: Reduce heat to medium. Add butter. Once melted, stir in garlic and red pepper flakes.
Cook 30–60 seconds until fragrant, not browned.
Deglaze: Pour in chicken broth. Scrape up any browned bits from the bottom of the pan. Simmer 1–2 minutes to reduce slightly.
Add cream and seasoning: Stir in heavy cream and Italian seasoning.
Bring to a gentle simmer. Season with a pinch of salt and a few grinds of pepper.
Cook the tortellini: Add tortellini to the pan. Stir to coat and spread in an even layer.
Cover and simmer on medium-low, stirring occasionally, until tortellini are tender and heated through, 4–6 minutes (a bit longer if frozen).
Finish the sauce: Turn heat to low. Stir in Parmesan gradually until melted and smooth. Add lemon juice.
If the sauce seems too thick, splash in more broth or a bit of cream. If too thin, let it gently simmer uncovered for a minute.
Wilt the greens: Fold in spinach. Cook 30–60 seconds until just wilted and vibrant.
Taste and adjust: Season with more salt, pepper, or lemon to balance the richness.
The sauce should be glossy and coat the tortellini.
Serve: Top with chopped parsley or basil and extra Parmesan. Serve hot.